You should look into Apache's Mod_Rewrite
Then, if you can enable the mod rewrite engine add the following line to your ht access file
RewriteRule ([a-zA-Z0-9_]+)/?$ $1.php [L]
What this will do is allow you to have somthing like
www.site.com/page1 and will turn it into www.site.com/page1.php
it will do this, for every page you call after the / and match it with the correct php file in the directory
the [L] on the end of the line, tells apache to stop scanning the htaccess file if a rulematch is found.
Bye
Sayian